Lamination is a common process for adhering films and sheets of various plastics, for example copolyesters. Typical film and sheet layers range in thickness from as thin as 0.5 mils to 1 inch, but thinner and thicker are possible. Typically branched polymers are used for processes that require high melt strength, for example, blown film, extrusion blow molding, and profile extrusion processes, in order to have a very high zero shear viscosity such that the material has melt integrity to minimize sagging under its own weight. In contrast, press lamination is typically completed at lower temperatures and the material is being heated while being supported. The temperatures for lamination are typically 20 to 60° C. above the glass transition temperature of polymer. The temperature is set to minimize flow of the polymer during the press lamination process while allowing the material in the different layers to achieve good adhesion. These press lamination processes are very dissimilar to processes compared to other processes, such as blown film or extrusion blow mold, in which branching agents are used typically at 100 to 200° C. above the glass transition temperature. Higher processing temperatures typically result in much less viscous polymer under the process conditions.
There exist a need for methods to form laminated article having embedded inclusions under conditions that reduce cycle time and improve dimensional stability of the polymer sheets during the lamination process.